Air intake system for supercharged automobile engine

Abstract

An air intake system for a supercharged automobile engine comprises a supercharger disposed on an air intake passage, a primary throttle valve disposed in a primary passage downstream of the supercharger and operatively coupled to an accelerator pedal, a secondary throttle valve disposed in a secondary passage and adapted to be controlled in association with the primary throttle valve, an auxiliary throttle valve in the secondary passage upstream of the secondary throttle valve, and an actuator operable to maintain the secondary throttle valve in a full open position when and so long as the load on the engine is equal to or larger than a predetermined medium load and to gradually open the secondary throttle valve with increase of the suction pressure when and so long as the load on the engine is smaller than the predetermined medium load.

We claim: 
     
       1. An air intake system for a supercharged internal combustion engine having a supercharger disposed on an air intake passage means, which system comprises, in combination: primary and secondary passages formed in a portion of the air intake passage means downstream of the supercharger;   a primary throttle valve disposed in the primary passage and operatively coupled to an accelerator pedal such that the selective opening and closure of said primary throttle valve can be controlled by the accelerator pedal;   a secondary throttle valve disposed in the secondary passage and operatively coupled to the primary throttle valve through a linkage mechanism;   an auxiliary throttle valve disposed in the secondary passage; and   an actuator for controlling the selective opening and closure of the auxiliary throttle valve in dependence on the suction pressure of air being sucked at a position downstream of the primary throttle valve or the throttle valves in the secondary passage, said actuator including means operable to gradually open the auxiliary throttle valve with increase of said suction pressure when and so long as the load on the engine is smaller than a predetermined medium load and to maintain the auxiliary throttle valve in a full open position when the load on the engine is equal to or larger than the predetermined medium load.   
     
     
       2. A system as claimed in claim 1, wherein said actuator comprises a diaphragm device adapted to be operated by the pressure inside the air intake passage means downstream of the throttle valves and including a spring which is caused to be in a full stroke by the suction pressure when the load on the engine is equal to or larger than the predetermined medium load, and a delay unit disposed on a pressure passage for the transmission of the pressure to the diaphragm device and operable to gradually open the auxiliary throttle valve. 
     
     
       3. A system as claimed in claim 1, wherein said actuator also includes means for holding the auxiliary throttle valve in the full open position when the engine speed is higher than a predetermined value. 
     
     
       4. A system as claimed in claim 2, wherein said actuator also includes means for holding the auxiliary throttle valve in the full open position when the engine speed is higher than a predetermined value. 
     
     
       5. A system as claimed in claim 4, wherein said means operable to hold the auxiliary throttle valve includes a valve operable in response to a signal from an engine speed sensor switch for introducing the atmospheric pressure to a pressure chamber of the diaphragm device. 
     
     
       6. A system as claimed in claim 2, wherein said delay unit includes a one-way valve for effecting a ready closure of the auxiliary throttle valve.